Billable transactions can be reduced if session ID is being used for Bing maps.
Details are on this link; http://msdn.microsoft.com/en-GB/library/ff859477.aspx
You must use the Bing Maps Key that you used to load the map control to request a session ID. This session ID is only valid for the map control session. For the web-based Bing Maps AJAX v7 and Silverlight controls, a session begins with the load of the map into a user’s browser and ends when the browser is closed or the user moves to a different page.
I am not sure about "session ends when the browser is closed or the user moves to a different page" .
Please correct me if i am wrong, i think on password protected sites session ends when user logs out. For an example; on my asp.net page, first i want to show 20 pin points or locations on one map depends on dataset results and then i want to show may be 10 results on one map. I can save the session id in user session the first time i made the request and use it again and again which will reduce the transactions to 1.
Do i need to use a new session id every time i close the map window? I am thinking about showing map on new window.